Is there a textured but unlit (full bright) viewport mode?
Yes, you can enable Shadeless in 3D view > Properties (N) > Shading while in textured view:



If you are in BI, this only works if using Multitexture shading:



If you are using GLSL in BI or material shading in Cycles, you'll have to use shadeless in the material settings for BI and a emission shader for cycles.